LibTest/collection/DoubleLinkedQueue/first_A01_t01.dart

// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

// @dart = 2.9

/// @assertion final E first
/// Returns the first element.
/// @description Checks that the method returns the first element of the queue.
/// @author kaigorodov

import "../../../Utils/expect.dart";
import "dart:collection";

main() {
  DoubleLinkedQueue queue = new DoubleLinkedQueue();
  
  queue.addFirst(1);
  Expect.isTrue(queue.first == 1);
  
  queue.addLast(2);
  Expect.isTrue(queue.first == 1);
  
  queue.addFirst(null);
  Expect.isTrue(queue.first == null);
}